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Outdoor air pollution is a significant global issue because it poses a major long-term health risk. A growing number of studies are conducted to develop local mitigation strategies for improving air quality. This review paper critically evaluates the available literature to provide a better understanding of potential local mitigation strategies and ascertain the methods for reducing local air pollution exposure. For these purposes, the first part of the review is categorized into three groups: (i) improving urban ventilation and turbulence level for pollutant dispersion. (ii) controlling source-receptor pathways by constructing barriers. (iii) capturing and mitigating air pollution by introducing pollutant sinks. Subsequently, a series of studies on optimization frameworks are summarized. It is found that surrogate model-based optimization frameworks efficiently handle multi-objective optimizations at a low computational cost. Finally, this review examines publications on the evaluation theory for pollutant dispersion to determine feasible methods for the removal of pollutants from urban areas. This study is useful for urban planners and architects responsible for decision-making. • Improving ventilation and turbulence are critical in mitigating air pollution. • Controlling source-receptor pathways is only beneficial at the pedestrian level. • Capturing air pollution by introducing sinks in strategic locations is effective. • Developing optimal frameworks is vital to enhance mitigation strategies' benefits. • Developing evaluation theories is required before new strategies are proposed. [ABSTRACT FROM AUTHOR]

Moving vehicles are the primary emission source of road pollution and the vehicle-induced turbulence (VIT) affecting the flow field in the street canyon. This paper used the dynamic mesh updating method to simulate the air pollution under the real situation of vehicle movement and exhaust emission in the street canyon. The dispersion characteristics of vehicular exhaust under various vehicle arrangements were analyzed. The personal intake fraction (P_IF) was introduced as an index to analyze the impact of factors such as vehicle speed and ambient wind velocity on the pollution exposure level of pedestrians. Based on the general assumptions in the study of street canyon pollution that vehicle-induced turbulence (VIT) is a continuous turbulence source and vehicle exhaust pollutants is a uniform pollution source, the conditions of the hypothesis are preliminarily explored. The research indicates that VIT can be regarded as a continuous turbulence source when vehicles maintain a "safe distance" on the road and form a stable traffic flow. Moreover, according to the range of dispersion of exhaust pollution, a "healthy distance" was proposed to guide driver to avoid direct impact of exhaust emitted from the vehicles in front. • The exhaust process of moving vehicles under various arrangement in the street canyon was visualized. • The factors affecting the dispersion of vehicle exhaust pollutants were analyzed. • The personal intake fraction (P_IF) was introduced to quantify the exposure of pedestrians. • The condition for treating VIT as a continuous turbulence source in the street canyon was determined. [ABSTRACT FROM AUTHOR]

During their rapid economic development and industrialization, megacities in the developing nations with high populations (especially in the east and south Asia) are plagued by severe air pollution problems (e.g., heavy haze), which impose a threat not only to public health but also to the sustainable development of society and the economy. To relieve the burden of air pollution for the general public, this article reviewed several geoengineering measures based on solar chimneys, which have the large-scale elimination ability on pollutants in the air, particularly for particulate matter. These geoengineering measures include driving the polluted air penetrate the planetary boundary layer into the troposphere to avoid the dramatic growth of concentrations of particulate matter, spraying water on the top of the solar chimney into the air to scavenge pollution, and intercepting fine particles in the air driven by the solar energy with large filters. Compared with traditional methods (e.g., giant spray trucks), those solar chimney geoengineering measures have the following advantages: 1) they can be operated 24 h a day, thus keeping the pollution removal function stable and continuous; 2) they are environment-friendly and can generate clean electricity to compensate for energy consumption; 3) they are also robust and operational with very low maintenance for a long period. Given the advantages of the solar chimney geoengineering measures and the economic and human health losses caused by air pollution, those geoengineering approaches deserve to be studied further and implemented in those countries that are suffering from heavy air pollution problems. [ABSTRACT FROM AUTHOR]

The acceleration of urbanization process, which triggered a series of environmental issues, has become increasingly prominent. Air pollution, especially atmospheric fine particulate matter (PM 2.5 ), is one of the most severe pollutions affecting the human health and living standard. In this article, a novel solar chimney with an inverted U-type cooling tower and a water spraying system (SCIUCTWSS) was proposed to mitigate the urban air pollution. In this system, an inverted U-type cooling tower was used to take place of the traditional chimney erected in the center of the collector; a water spraying system was installed at the turning point of the inverted U-type cooling tower to enhance the driving force; a filtration screen is placed near the entrance of the collector to filter out PM 2.5 and large particulate matter from the airflow. The clean air out of the system’s outlet can immediately improve the air quality in the spectrum of human activity. A mathematical model to describe the fluid flow, heat transfer of the system was further developed. Influence of injected water from the water spraying system on the pressure, velocity, temperature, and air density distributions were analyzed. The numerical simulation results indicated that water injection is efficient that can strengthen the natural convection and has a positive influence on the heat transfer process within the system. This proposed SCIUCTWSS in this article is able to process atmospheric air at a volume flow rate of 810 m 3 /s, corresponding to the volume of 69,984,000 m 3 of air to be cleaned in one day. However, in view of the economic and human comfort, the amount of injected water should be taken into comprehensive consideration. [ABSTRACT FROM AUTHOR]